Process for electrodeposition of graft copolymer

ABSTRACT

A polyamine/epoxy ester graft copolymer having an acrylic polyamine backbone with secondary amine and hydroxy functionality, part of which is terminal primary hydroxy groups, onto which is grafted an epoxy-fatty acid ester. The ester is an epoxy resin reacted with a fatty acid resulting in a monoepoxide ester with one or less epoxy group per acid group. The ester is reacted with part of the secondary amine on the acrylic backbone. This system can be formulated to a nearly-neutral pH cathodic dispersion with good cure response at 150°-175° C. using conventional aminoplast crosslinkers.

This is a division, of application Ser. No. 902,887, filed May 9, 1978.

BACKGROUND OF THE INVENTION

The present invention relates to graft copolymers and compositionssuitable for cathodic electrodeposition of polymeric coatings.Furthermore, it relates to a method of cathodic electrodeposition ofsuch graft copolymers.

It is known that organic coatings can be electrodeposited either on ananodically-charged conducting substrate or on a cathodically-chargedsubstrate. Although most of the earlier work in electrodeposition wasdone with anodic deposition, that type of process has certaindisadvantages. Anodic electrodeposition is normally done in a coatingbath having a basic pH. The pH decreases at the surface being coated,creating conditions which, when combined with the electrolytic action ofthe coating bath, can cause the dissolution of substrate metal ions andtheir subsequent deposition in the coatings being formed. This can be asource of staining and diminished corrosion resistance. Also,electrolysis tends to attack preformed phosphate coatings on the anode.Furthermore, oxygen formed at the anodic substrate being coated cancause a variety of difficulties such as degradation of coatings byoxidation.

Electro-endoosmosis tends to expel water from anodic coatings beingformed, leading to low water retention with about 85-95% solids in thecoatings. This is an advantage over cathodic coating in which thisphenomenon would not be expected to be helpful. (Parts and percentagesherein are by weight except where indicated otherwise.)

Cathodic electrodeposition has developed more slowly, due in part to theacidic pH needed for the bath. Also, water tends to be drawn into thecoatings and held there, along with acid residues from the bath. It isapparent that this can lead to difficulties in the coatings. In contrastto the oxygen formed at anodes in anodic electrodeposition, hydrogen isformed at the cathode in cathodic electrodeposition. Even though thishydrogen can cause pinholes in coatings, it, of course, does not causeoxidative film degradation.

Processes and compositions for the cathodic electrodeposition of paintsare described in U.S. Pat. No. 2,345,543--Wohnsiedler, et al. (1944),which uses a cationic melamine-formaldehyde resin, and in U.S. Pat. No.3,922,212--Gilchrist (1975), among others. Gilchrist is directed to aprocess for supplementing the bath composition with a make-up mixture ofmaterials containing an ionizing acid that is not consumed at as fast arate as the resin. The acid is present in the make-up at lowerconcentrations than are used in the bath, so as not to build up theconcentration of the acid in the bath. Gilchrist uses particularaminoalcohol esters of polycarboxylic acids and discloses that acrylicpolymers can be codeposited with zinc phosphate from solution on acathodic substrate at low pH's such as 2.7 with phosphoric acid orvolatile organic acids as the ionizing acid. Higher pH levels would bedesirable for minimizing corrosion of coating equipment, especially ifvolatile nonpassivating acids are used for solubilization instead ofphosphoric acid.

Two U.S. patents dealing with nitrogen-based copolymers and theircathodic electrodeposition are U.S. Pat. Nos. 3,455,806 and 3,458,420,both to Spoor, et al. (1969). Cathodic sulfonium systems are describedby Wessling et al. on pages 110-127 of "Electrodeposition of Coatings,"Ed. E. F. Brewed, American Chemical Society (1973).

Electrodeposition processes have been frequently described in theliterature. Two useful reviews of the technology are: "Electro-paintingPrinciples and Process Variables," Brower, Metal Finishing, September,1976, p. 58; and "Coatings Update: Electrocoating," Americus, Pigmentand Resin Technology, August, 1976, p. 17.

Dual cure cathodic electrocoating compositions are described in U.S.Pat. No. 4,070,258--McGinniss (1978) using a polymer with pendanttertiary amine groups, pendant mercaptan groups, anethylenically-unsaturated carbonyl crosslinking agent and aphotosensitizer. The deposited compositions are cured by using both heatand ultra-violet radiation. U.S. Pat. No. 4,066,523--McGinniss (1978) issimilar except it uses a bis-maleimide crosslinking agent.

U.S. Pat. No. 4,066,525--Woo and Evans (1978) provides a cathodicelectrocoating process using an aqueous dispersion of (a) an ionizedreaction product of an epoxy resin and a monoamino alcohol or phenol,said reaction product also having a pendant hydrocarbon group, (b) anacid-functional aminoplast resin, and (c) a water-soluble acidsolubilizer.

Cathodic electrocoating systems are based on alkaline cationic resinsthat are solubilized or dispersed in water with the aid of an acid. Inorder to minimize corrosion of tank construction materials, it has beenthe aim of the industry to develop technology that will result incathodic systems that are stable in water at close to neutral pH. Thiscould be achieved by incorporating in the cationic resin strong alkalinefunctionality such as quarternary ammonium salts, primary or secondaryamines, or combinations thereof and solubilizing the resin in water byneutralizing the amine with a weak acid--usually an organic acid.Because of the high basicity of the deposited film, one of the majorproblems in the development of such cathodic systems has been to obtainadequate cure, using conventional aminoplasts as crosslinking agents, atrelatively low temperatures of 150°-175° C., which are important forvarious applications such as in the automotive industry. The difficultyin obtaining adequate cure is caused by the fact that the crosslinkingof conventional aminoplasts of the melamine benzoguanamine or ureaformaldehyde type requires acid catalysis and is strongly inhibited by abasic environment. For this reason, technologies have been developed forcathodic systems that use partially or fully blocked isocyanates as thecuring agents. The crosslinking of isocyanates is base-catalysed andrequires a basic environment. Isocyanate crosslinking has severalshortcomings, including the need for usually high temperature orcatalysts to unblock the isocyanate, high cost, and toxicity of rawmaterials and possibly of oven effluent during bake. It has been feltthat the cathodic electrocoating technology will be at a disadvantage ifit is restricted to such mechanisms of cure.

None of the prior art provides a fully-satisfactory composition forcathodic electrocoating at nearly neutral pH with the ability to cure atrelatively low temperatures and times, with or without a crosslinkingagent.

SUMMARY OF THE INVENTION

The present invention provides a graft copolymer comprising amono-epoxide portion grafted onto an acrylic-amine backbone portion,which portions consist essentially of, by weight based on the graftcopolymer, about:

(a) 25-60%, preferably 28-37%, of an acrylic-amine backbone copolymercontributing:

14.7-35%, preferably 16.5-21.8%, of secondary amine methacrylate,preferably tertiary butyl aminoethyl methacrylate, giving 0.08-0.2equivalent of amine per 100 grams of graft copolymer,

7-17%, preferably 7.8-10.4%, of hydroxy-functional acrylate ormethacrylate, preferably hydroxy-ethyl methacrylate,

3-7.3%, preferably 3.4-4.4%, of ethyl acrylate or methyl methacrylate,and

0.3-0.7%, preferably 0.3-0.4%, mercapto-ethanol, giving primary terminalhydroxy functionality,

graft polymerized with (b) and (c):

(b) 33-60%, preferably 54-59%, of an epoxy-fatty acid copolymer of acondensation polymer of approximately equimolar proportions ofepichlorohydrin and bisphenol-A reacted with fatty acids, preferablydehydrated castor oil fatty acid or 1,2-hydroxy stearic fatty acid.Linseed oil fatty acid, tall oil fatty acid or amine-containing fattyacids such as Ethomeen, produced by Armour Industrial Chemical Co., canalso be used. The mole ratio of epoxy resin to fatty acid should be1/1.4-1.7 so that the epoxy ester has less than one epoxy equivalent permolecule, and

(c) 7-15%, preferably 9-13%, of a glycidyl ester of a tertiarycarboxylic acid containing 7-9 carbon atoms, preferably versatic acid,such as Cardura E, produced by Shell Oil Co.

A preferred embodiment consists essentially of, by weight based on thegraft copolymer, about:

(a) 33% of an acrylic-amine backbone copolymer contributing:

19.4% of tertiary butyl aminoethyl methacrylate, giving about 0.1equivalent of amine per 100 grams of graft copolymer,

9.3% hydroxyethyl methacrylate,

4% ethyl acrylate, and

0.3% mercaptoethanol,

graft copolymerized with (b) and (c):

(b) 55% of an epoxy-fatty acid copolymer of a condensation polymer ofequimolar proportions of epichlorohydrin and bisphenol-A reacted withdehydrated castor oil fatty acid at a molar ratio of 1/1.7 epoxy resinto fatty acid, and

(c) 12% of Cardura E glycidyl ester.

After the grafting process, there are 0.05 equivalents per 100 g ofgraft copolymer of tertiary amine (a reaction product of the epoxy resinwith the secondary amine) and 0.057 equivalents of secondary amine. Itis important that the level of secondary amine not drop below 0.04equivalents per 100 g of graft copolymer in order to obtain a stabledispersion at pH 6-7.

Another embodiment of this invention consists essentially of, by weightbased on the graft copolymer, about:

(a) 25% of an acrylic-amine backbone copolymer contributing:

14.7% of tertiary butyl aminoethyl methacrylate, giving about 0.008equivalent of amine per 100 grams of graft copolymer,

7% hydroxyethyl methacrylate,

3% ethyl acrylate, and

0.3% mercaptoethanol

graft polymerized with (b) and (c):

(b) 70% of an epoxy-fatty acid copolymer of a condensation polymer ofequimolar proportions of epichlorohydrin and bisphenol-A reacted withdehydrated castor oil fatty acid at a molar ratio of epoxy resin tofatty acid of 1/1.7, and

(c) 5% of Cardura E glycidyl ester.

After the grafting process, there are 0.03 equivalents of tertiary amineand 0.05 equivalents of secondary amine per 100 g of graft copolymer.

The invention also provides coating compositions of such graftcopolymers with a nitrogen resin crosslinker, preferablybenzoguanamine-formaldehyde or urea-formaldehyde resins; as an ionizingagent, organic acid volatile at the curing temperature, preferablylactic, acetic, succinic or citric acids, present in an amount to give apH of 6.0 to 7.0; and a liquid carrier, preferably an aqueous liquidcarrier. Since the graft copolymers can crosslink themselveseffectively, the nitrogen resin crosslinker can be omitted.

DETAILED DESCRIPTION OF THE INVENTION

In order to increase the pH of a cathodic electrocoating system withoutadversely affecting the cure response, using conventional aminoplastssuch as benzoguanamine, urea formaldehyde and melamine formaldehyderesins as crosslinkers and obtaining satisfactory cures at about150°-175° C., a new approach in the stabilization of the cathodicdispersion has been undertaken.

The approach minimizes the basicity inside the dispersion particle andmaximizes it on the outside of the particle by controlling the coilingcharacteristics of the cationic polymer. This can be achieved byincorporation of the amine functionality on a flexible hydrophilicbackbone with pendant hydrophobic epoxy ester groups so that most of thebasic groups will be on the outside of the dispersion particle formaximum pH in the water phase and minimum basicity inside the particlefor minimum inhibition of cure response of the deposited film.

The present invention provides cathodic systems which avoid limitationsof isocyanate systems and have good cure response with conventionalaminoplasts at temperatures of 150°-175° C. Dispersions with a pH of 6-7are used, giving a deposited film with a pH of 7-10. The invention isbased on a hydrophilic/hydrophobic graft system, with the hydrophilicbackbone being a polyamine (primary and/or secondary) with hydroxyfunctionality, with some of the hydroxy groups preferably positioned asterminal hydroxy functionality at the end of the backbone molecule. Sucha polyamine is preferably made from vinyl unsaturated acrylate and/ormethacrylate esters of acrylic and/or methacrylic acid. This permitsgood control over the composition and structure of the backbone foroptimum properties.

The polyamine backbone could also be made from other constituents suchas polypropylene amine and/or polypropylene imine partially reacted withethylene oxide in order to add further hydroxy functionality.

The hydrophobic part that is grafted on to the polyamine backbone ispreferably an epoxy ester that is the reaction product of an Epon epoxyresin, an adduct of bisphenol-A and epichlorohydrin made by Shell OilCo., with a fatty acid at molar ratios of epoxy/fatty acid of 1/1.4-1.7.The epoxy ester is formed by the reaction of the fatty acid with theepoxy group in the presence of a catalyst. The residual epoxy groupspresent in the epoxy ester are used to graft the epoxy ester on to thepolyamine backbone by reacting the epoxy group with the aminefunctionality. Primary amines will become secondary and secondary willbecome tertiary after the reaction with the epoxy functionality. Thepresence of tertiary amines on the backbone is avoided in order tominimize the formation of quarternary ammonium salts that have anadverse effect on the electrocoatability of the system. As can be seenfrom the above epoxy/fatty acid ratios, not every epoxy ester moleculeis grafted on to the polyamine backbone. This increases the electricalinsulating properties of the wet electrodeposited film in the bath,resulting in the ability to deposit the paint deeper in blind holes,known as high throwing power.

Desirable characteristics of the hydrophobic/hydrophilic graft thatpermit the use of conventional aminoplasts with good cure responseinclude the following:

(a) The hydrophilic backbone, the hydroxy-containing polyamine, acts asa stabilizer by wrapping itself around the hydrophobic portion of thegraft copolymer when dispersed in water. This gives maximum pH in thewater phase and maximum dispersion stability with minimum amount ofamine functionality. The alkaline functionality is mostly on the outsideof the particle, and there is very little inhibition to cure in thelarger hydrophobic portion of the particle, the epoxy ester graft. Bycrosslinking the hydrophobic portion of the total system, any backboneconnected to the epoxy ester through the graft mechanism becomes part ofthe crosslinked resin. Even the portions of the polyamine backbone thatare not grafted with the epoxy ester have a self-crosslinkingcapability, mainly by transesterification of the hydroxy functionalitywith the acrylate esters. Such a reaction is catalyzed by the strongbasic environment caused by the amine functionality. The backbone willself-crosslink by the above mechanism readily at relatively lowtemperatures of 120°-150° C.

(b) In order to obtain a stable dispersion at pH 6-7, part of the aminefunctionality is primary and/or, preferably, secondary amines. Theminimum desirable amount of such an amine is 0.04-0.05 equivalents per100 gm of total graft system.

(c) The hydroxy functionality on the polyamic backbone has a veryimportant role. It contributes the hydrophilicity of the backbone,discussed in (a) above, and it introduces crosslinking sites for bothtransesterification in the preferred acrylic polyamine described in thisinvention and for crosslinking by the aminoplast mechanism. The minimumdesirable level of hydroxy functionality is 0.4 equivalents per amineequivalent in the backbone.

A preferred composition of the invention can be made as follows, withthe structural formulae schematically indicated.

The acrylic polyamine backbone is made by copolymerizing, in parts byweight:

12 ethyl acrylate/59 tertiary butyl aminoethyl methacrylate/28hydroxyethyl methacrylate/1 mercaptoethanol. ##STR1##

The epoxy ester graft is made by reacting 1 mole Epon 1004 and 1.7 molesdehydrated castor oil fatty acid. ##STR2##

The graft copolymer is made by copolymerizing, in parts by weight:

33 acrylic backbone/55 epoxy ester/12 Cardura E. ##STR3##

A coating composition is made from a clear formulation, in parts ofsolids content by weight, of:

70 graft copolymer resin/30 XM 1125 crosslinker, which is neutralized to50% of stoichiometric with lactic acid, with water added.

More specifically, one can use 222 parts graft copolymer resincontaining the codispersed diadduct of epoxy and fatty acid, 70 parts XM1125 crosslinker, 9 parts 85% lactic acid, and 1700 parts water.##STR4##

Coating compositions of the invention can be cathodicallyelectrodeposited either on pretreated metal such as phosphatized steelor on bare metal such as steel which has been cleaned but notphosphatized. It can also be used on other metal substrates containingzinc, such as galvanized steel, as well as on aluminum and variousalloys.

The lack of practical success of several previous cathodicelectrodeposition painting processes is due at least in part to theamount of water that is held in the resin coating and the acids andsalts that are dissolved in that water, not readily removable from thecoating. The water can lead to coating failure by various mechanisms,and the acid residues can encourage subsequent corrosion, eitherdirectly or by providing a hygroscopic material in the coating whichencourages penetration of water and other corrosive agents.

In contrast to the useful effect of electroendoosmosis at the anode inanodic electrodeposition of paint which tends to expel water from ananodic coating, water is not electrically expelled from a cathodiccoating and may actually be drawn into the coating by electrical forces.However, water held in a cathodic coating can be particularlyundesirable. To minimize such effects, the present invention providesresins with a degree of hydrophobicity and hardness or denseness of thecoating which combine to expel water from the coating as the coating isformed.

The desirable effects of the invention are achieved by using certainhydrophobic graft copolymers containing in their backbone portions oftertiary and secondary amine functionality. Such functionalityintroduces an alkaline mechanism of adhesion of the resin coating to thesubstrate even after heating the deposited coatings to cause them tocrosslink. This has been found to improve corrosion resistance ofcoatings when compared to coatings using an acidic mechanism of adhesionintroduced by carboxylic groups such as in an anodic electrocoatingsystem. This is an advantage over cathodic systems stabilized by oniumgroups, such as sulfonium and quarternary ammonium, in whichhydrophobicity is only developed after thermal decomposition of theonium groups. Thermal decomposition of onium groups during crosslinkingof the film would also make them unavailable for enhancing adhesion ofthe resin coating to the substrate.

In the process of the invention, although there are advantages in usinglive entry, in which the coating voltage is applied while the articlesto be coated are being immersed into the bath, it will be apparent thatreduced voltage can be applied upon entry if desired for certain specialeffects. However, the additional electrical apparatus required forreduced voltage entry is not normally necessary or desirable. It isdesirable for the coated substrate to be removed from the bath with thecoating voltage still applied or soon after it is turned off.

For operating electrocoating baths of the invention, the tank can belined with an organic coating resistant to the mildy-acidic pH of thebath, and stainless steel or plastic piping and pump parts can be usedto minimize corrosion. However, carbon steel parts and piping usuallycan be used as a material of construction without a corrosion problem.

Ultrafiltration can be used by recirculating the bath components torinse contaminants and drag-out from the coated parts. Either membranesand ordinary flushed anodes or an acid deficient feed can be used, as isknown in the art, to minimize the build-up of acid in the coating bath.

Although an uncoated tank can be used as the anode, in commercialpractice one would normally use stainless steel anodes having a surfacearea smaller than that of the cathodic substrate which is to be coated.This gives a favorable current density distribution.

In the novel electrocoating process, the metal article providing thesubstrate to be coated is immersed in a bath of an electrocoating cell.The bath is an aqueous dispersion of preferably about 2-35% by weight ofa cationic film-forming polymer at least partially neutralized with anorganic acid which is volatile at the temperatures used to crosslink thepaint film. Suitable acids include lactic, acetic, succinic and citricacids. Preferably lactic acid is used in an amount of from 30% of thatrequired for stoichiometric reaction of the hydrogen of the acid withall of the available amine group bonds in the polymer to about 100% ofstoichiometric. It is more preferably to use about 50%. The use of lessthan about 30% of the stoichiometric amount of acid can lead toinstability in the bath. More than 100% can lead to undesirable excessacidity in the bath with consequent corrosion of coating equipment. Thepreferred pH of the coating bath is about 6.5-7.0.

The metal article is connected to the negative side of a direct current(D.C.) power source to become the cathode of the cell. A voltage ofabout 1 to 550 volts is passed through the cell for the full dwell timeof the article in the bath, about 0.01 to 5 minutes, preferably 2minutes, and a coating of the cationic polymer is deposited. When thecoating reaches the desired thickness, the article is removed from thebath. Preferably, the article is rinsed with water and/or withultra-filtrate taken from the bath, to remove excess coating. Then thearticle is dried at ambient temperatures or baked for about 5 to 40minutes at about 100° to 200° C., preferably about 30 minutes at 175°C., to give a finished coating about 0.1 to 5 mils thick. Typicalefficiencies of about 30 mg film solids deposited per coulomb ofelectricity are obtained.

The current density used in the electrocoating cell generally does notexceed 1.85 amperes/cm² (0.3 amperes/in²) of anode surface which isimmersed in the bath, and it is preferable to use lower currentdensities. In the deposition of the cationic film-forming polymer,voltages of 5 to 400 for 0.25 to 2 minutes are preferred to form ahigh-quality finish.

Coating compositions of the present invention can contain pigments. Thepigments are normally added to the composition in the usual manner byforming a mill base or pigment dispersion with the pigment and theafore-mentioned cationic film-forming polymer or anotherwater-dispersible polymer or surfactant. This mill base is then blendedwith additional film-forming constituents and the organic solvents. Whenthe mill base is subsequently acidified and dispersed in water, thepolymers tend to wrap themselves around the pigments. This has theeffect of preventing destabilization of the dispersion or otherundesirable effects that could come from using a basic pigment such asTiO₂ or lead silicate in an acid stabilized dispersion. Other pigmentsthat could be used include metallic oxides such as zinc oxides, ironoxides, and the like, metal flakes such as aluminum flake, metalpowders, mica flakes with and without surface treatment such as withtitania and carbon black, chromates such as lead chromates, sulfates,carbon black, silica, talc, lead silicates, aluminum silicates includingchina clay and finely divided kaolin, organic pigments and solubleorganic dyes.

Aside from cathodic electrodeposition, the novel coating compositions ofthe present invention can also be applied by any conventional methodsuch as spraying, electrostatic spraying, dipping, brushing, flowcoatingand the like. Reaction of the amine groups of the polymer with an acidis generally not necessary when the coating composition is to be usedfor purposes other than electrodeposition. Other organicthermally-decomposable acids, such as formic acid, can be used to obtainwater solubility for such purposes. The coating would then be baked forabout 5 to 40 minutes at about 150° to 200° C. to give coatings of about0.1-5 mils thickness. When applied by cathodic electro-deposition,coating compositions of the invention are preferably applied to givedried thicknesses of about 0.8-1.2 mils.

A valuable attribute of this invention is the ability to crosslink acationic resin which is alkaline in nature with conventional nitrogenformaldehyde resins which usually require an acidic environment as acatalyst, with curing at temperatures of 150°-175° C. A crosslinkingagent which can be water dispersed along with the film-formingconstituent is used in the coating composition. Based on the proportionsof solids in the bath, which are roughly equal to the proportions ofsolids in the film, about 60 to 95%, preferably about 70%, of cationicfilm-forming polymer are used along with about 5 to 40%, preferablyabout 30%, of crosslinking agent.

Typical crosslinking agents that can be used with the invention aremelamine formaldehyde, alkylated melamine-formaldehyde resins such ashexakis-(methoxymethyl) melamine and partially-methylated melamineformaldehyde resins, butylated melamine formaldehyde resins, methylatedurea-formaldehyde resins, urea-formaldehyde resins, phenol-formaldehydeand the like. One particularly useful crosslinking agent which forms ahigh-quality product with the cationic polymers is abenzoguanamine-formaldehyde resin used in conjunction with aurea-formaldehyde resin such as Beetle 80, produced by American CyanamidCo. A preferred benzoguanamine formaldehyde resin is XM 1125, alsoproduced by American Cyanamid Co.

When the novel compositions of this invention are used as primers overmetals including treated and untreated steel, aluminum and other metals,conventional acrylic enamels, acrylic dispersion enamels and othercoating compositions can be applied directly as topcoats over suchprimers. Acrylic lacquers, acrylic dispersion lacquers, and acrylicpowder coatings can be applied over the novel compositions, but asuitable intermediate coat such as a sealer can be used to improveadhesion of the lacquer or powder topcoats to the primer.

The epoxy graft used in compositions of the invention contributessufficient hydrophobicity to the polymer so that the electrodepositedfilm contains at least about 83% solids, and preferably 85 to 95%solids. Although such high solids levels are not uncommon foranodically-deposited coatings, they are not readily achieved in cathodicelectrodeposition because of the amount of water usually entrapped.

Compositions of the invention can include additional adjuvants that donot materially change the basic and novel characteristics of theinvention and thus are within the scope of "consisting essentially"terminology. Some such adjuvants are thickeners, defoamers, pigments,microgels, pigments dispersants, polymeric powders, microbiocides, andcoalescing solvents. Typical coalescing solvents which might be used ata concentration of about 0.5% of the total bath volume are ethyleneglycol monobutyl ether, diethylene glycol monobutyl ether, cyclohexanoland hexylcellosolve.

Although it is difficult to meaningfully quantify the softness orhardness of the resin, it is known that certain resins of the inventionhave a degree of hardness which is useful in combination with thehydrophobicity characteristics of the resins in forcing water out offilms to obtain the indicated levels of retained water and acid.

The molecular weights of polymers of the invention are generally notcritical. However, typical average molecular weights determined by gelpermeation chromatography are: for the acrylic-amine backboneportion--10,000 to 12,000, for the epoxy-fatty acid portion--1,500 to3,000, and for the reacted graft copolymer--about 12,000.

Although thoughts are expressed herein on why and how the advantages ofthe invention are obtained, the invention is defined by the claims anddoes not depend upon theories.

Specific examples will now be given of the preparation of graftcopolymers of the invention and their use in cathodic electrodepositionprocesses of the invention.

BEST MODE

Depending on the properties sought, the invention has various bestmodes, illustrated by the examples.

EXAMPLE I

A black primer coating composition is prepared and used as follows:

Part I and Part II describe the two resin compounds that are graftpolymerized and used with the pigment dispersions of Part III in thepaint of Part IV.

PART I

This part describes the preparation of an epoxy ester for graftcopolymerization.

The following ingredients are charged into a reaction vessel equippedwith a stirrer, thermometer, reflux condenser and a heating mantle toform an epoxy ester resin solution:

    __________________________________________________________________________    Portion 1                     Parts by Weight                                 __________________________________________________________________________    Epoxy resin (Epon 1004)       1250.00                                         Dehydrated castor oil         250.00                                          fatty acid                                                                    Ethylene glycol monoethyl-    500.00                                          ether                                                                         (Epon 1004 is an epoxy resin of the formula                                    ##STR5##                                                                     where m is an integer sufficiently large to                                   provide a Gardner-Holdt viscosity at 25° C. of                         G-I measured in a 40% weight solids polymer                                   solution using ethylene glycol monobutyl ether                                solvent. The resin has an epoxide equivalent                                  of 950-1050 and is produced by Shell Oil Co.)                                 __________________________________________________________________________

    ______________________________________                                        Portion 2            Parts by Weight                                          ______________________________________                                        Benzyl trimethylamonium                                                                            2.50                                                     hydroxide                                                                     ______________________________________                                    

Portion 1 is charged into the reaction vessel, blanketed with nitrogenand heated to about 128°-140° C. to melt the resin. Portion 2 is thenadded, and the ingredients are heated to about 135°-145° C. for about 5hours with constant agitation until the reaction mixture has an acidnumber of 0.01.

The resulting epoxy ester resin solution has a solids content of about75%, an acid number no higher than 0.01, an epoxide equivalent of3800-4500, and a Gardner-Holdt viscosity of F-H at 25° C. in a 40%solids polymer solution using ethylene glycol monoethyl ether solvent.

PART II

This part describes the preparation of an acrylic resin and the graftpolymerization of the epoxy ester described above onto it.

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Portion 1                                                                      Isopropanol          400.00                                                  Portion 2                                                                      Ethylacrylate        75.00                                                    Tertbutylaminoethyl  370.00                                                   methacrylate                                                                  Hydroxyethyl methacrylate                                                                          175.00                                                   Mercaptoethanol      10.00                                                   Portion 3                                                                      Isopropanol          100.00                                                   Methylethyl ketone   25.00                                                    Azobisisobutyronitrile                                                                             10.00                                                   Portion 4                                                                      Methylethyl ketone   8.00                                                     Azobisisobutyronitrile                                                                             1.00                                                    Portion 5                                                                      Ethylene glycol monoethyl                                                                          533.00                                                   ether                                                                        Portion 6                                                                      Epoxy ester prepared in                                                                            1356.00                                                  Part 1                                                                        Etylene glycol monoethyl                                                                           350.00                                                   ether                                                                         Cardura E-10 (glycidyl                                                                             340.00                                                   ester of epichlorohydrin                                                      reacted with versatic acid                                                    911, produced by Shell Oil                                                    Co.)                                                                          Benzyltrimethylammonium                                                                            10.00                                                    hydroxide                                                                    ______________________________________                                    

Portion 1 is charged into a reaction vessel, equipped as describedabove, and is heated to its reflux temperature. The reaction mixture isheld under nitrogen during the entire reaction. Portions 2 and 3 areseparately premixed and added slowly simultaneously over a 60-minuteperiod while maintaining the reaction mixture at its reflux temperature.The reaction is continued for an additional 60 minutes. The Portion 4 isadded, and the reaction mixture is held at its reflux temperature for anadditional 30 minutes. Stripping of the reaction solvent is conductedsimultaneously with the addition of Portion 5 which is to replace thereaction solvent. When 533.00 parts of solvent are stripped and all ofPortion 5 is added to the reaction vessel, Portion 6 is added and thetemperature is brought to 115°-117° C. and maintained for 4 hours withcontinuous agitation. At the end of that period the epoxy number isdetermined. When the epoxy equivalent is zero or less than 1 epoxy unitper 500,000 gm, the reaction is finished. The solids content is 60%, andthe Gardner-Holdt viscosity at 25% reduction of solids with ethyleneglycol monoethylether is U to X.

PART III

A black pigment dispersion is prepared as follows:

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Solution polymer prepared                                                                           371.00                                                  in Part II                                                                    Ethylene glycol monoethyl-                                                                          31.00                                                   ether                                                                         Carbon black pigment  31.80                                                   ______________________________________                                    

The above ingredients are premixed and charged into a conventional sandmill and ground at a rate of 30 gallons per minute while controlling thetemperature of the mixture below 70° C. The resulting carbon blackdispersion has about 58% solids content.

An extender pigment dispersion using diatomaceous earth as the extenderpigment is prepared as follows:

    ______________________________________                                                            Parts by Weight                                           Solution polymer prepared                                                                           225.00                                                  in Part II                                                                    Ethylene glycol monoethyl-                                                                          110.00                                                  ether                                                                         Diatomaceous earth pigment                                                                          206.00                                                  ______________________________________                                    

The above ingredients are premixed and charged into a conventional sandmill and ground at a rate of 30 gallons per minute while controlling thetemperature of the mixture below 70° C. The resulting diatomaceous earthdispersion has about 63% solids.

PART IV

The electrocoating composition of a flated black paint is prepared asfollows:

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Portion 1                                                                      Resin solution of Part II                                                                          373.00                                                   Black pigment dispersion                                                                           97.00                                                    of Part III                                                                   Diatomaceous earth pigment                                                                         440.00                                                   dispersion of Part III                                                        Benzoguanamine formaldehyde                                                                        76.00                                                    soluton (XM 1125 produced                                                     by American Cyanamid Co.,                                                     85% in ethylene glycol                                                        monobutyl ether)                                                              Urea formaldehyde resin                                                                            100.00                                                   (Beetle-80, produced                                                          by American Cyanamid Co.)                                                    Portion 2                                                                      Deionized water      632.00                                                   Lactic acid 85% solution                                                                           10.00                                                    in water                                                                     ______________________________________                                    

Portion 1 is added into a mixing vessel, heated to 150° F. and mixed for3 hours, maintaining a temperature of 150° F. Portion 2 is added intoanother mixing vessel mixed for 10 minutes, and Portion 1 is added intoPortion 2 with continuous agitation. The pigmented water dispersion ismixed for 2 hours and diluted to about 15% solids with deionized water.

Industrial Applicability

The electrocoating composition, having a pH of 6.2-6.5 and aconductivity of 700-1000 micromhos, is charged into a stainless steeltank for electrodeposition. An untreated cold rolled steel panel or aphosphatized steel panel is positioned in the center of the tank,electrically connected to the negative side of a DC power source, andforms the cathode of the electrocoating cell. The tank is connected tothe positive side of a DC power source and forms the anode of the cell.A direct current of 150-300 volts is applied to the cell for 2 minutesat an ambient temperature of 20°-25° C., and a paint film of about 0.6mils is deposited on the panel. The coated metal panel is removed fromthe electrocoating cell, washed and baked at about 160° C. for 30minutes. The resulting primer film has excellent adhesion to the metalsubstrate, is hard and has very good corrosion and saponificationresistance over bare cold rolled steel and phosphatized steel. Anacrylic enamel adheres to the primer film, and conventional acryliclacquers can be applied with a conventional sealer coat over the primerto form a high-quality finish.

Typical deposited films contain 90 to 95% solids and 10 to 12% of theconcentration of the lactic acid present in the bath.

This coating composition is particularly useful for priming automobileand truck bodies by electrodeposition for maximum corrosion protectionover all parts of the car including areas of poor phosphate pretreatmentor no pretreatment at all.

EXAMPLE II

A black primer coating composition is prepared and used as follows:

Part I and Part II describe the two resin compounds that are graftpolymerized and used with the pigment dispersions of Part III in thepaint of Part IV.

PART I

This part describes the preparation of an epoxy ester for graftcopolymerization.

The following ingredients are charged into a reaction vessel equippedwith a stirrer, thermometer, reflux condenser and a heating mantle toform an epoxy ester resin solution:

    __________________________________________________________________________    Portion 1                     Parts by Weight                                 __________________________________________________________________________    Epoxy resin (Epon 1001)       1500.00                                         __________________________________________________________________________    (Epon 1001 is an epoxy resin of the formula                                    ##STR6##                                                                     where m is an integer sufficiently large to                                   provide a Gardner-Holdt viscosity at 25° C. of                         D-G measured in a 40% weight solids polymer                                   solution using ethylene glycol monobutyl ether                                solvent. The resin has an epoxide equivalent                                  of 450-550 and is produced by Shell Oil Co.)                              

    ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Portion 2                                                                      Dehydrated castor oil                                                                             630.00                                                    fatty acid                                                                    Benzyl trimethylamonium                                                                           3.00                                                      hydroxide                                                                    Portion 3                                                                      Ethylene glycol monoethyl                                                                         710.00                                                    ether                                                                        ______________________________________                                    

Portion 1 is charged into the reaction vessel, blanketed with nitrogenand heated to about 128°-140° C. to melt the resin. Portion 2 is thenadded, and the ingredients are heated to about 150°-160° C. for about 3hours with constant agitation until the reaction mixture has an acidnumber of 0.01. Portion 3 is added, and the ingredients are cooled andfiltered.

The resulting epoxy ester resin solution has a solids content of about75%, an acid number no higher than 0.01, an epoxide equivalent of3500-4200, and a Gardner-Holdt viscosity of D-F at 25° C. in a 40%solids polymer solution using ethylene glycol monoethyl ether solvent.

PART II

This part describes the preparation of an acrylic resin and the graftpolymerization of the epoxy ester described above onto it.

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Portion 1                                                                      Isopropanol          400.00                                                  Portion 2                                                                      Methylmethacrylate   75.00                                                    Tertbutylaminoethyl  370.00                                                   methacrylate                                                                  Hydroxyethyl methacrylate                                                                          175.00                                                   Mercaptoethanol      10.00                                                   Portion 3                                                                      Isopropanol          100.00                                                   Methylethyl ketone   25.00                                                    Azobisisobutyronitrile                                                                             10.00                                                   Portion 4                                                                      Methylethyl ketone   8.00                                                     Azobisisobutyronitrile                                                                             1.00                                                    Portion 5                                                                      Ethylene glycol monoethyl                                                                          533.00                                                   ether                                                                        Portion 6                                                                      Epoxy ester prepared in                                                                            1696.00                                                  Part 1                                                                        Ethylene glycol monoethyl                                                                          350.00                                                   ether                                                                         Benzyltrimethylammonium                                                                            10.00                                                    hydroxide                                                                    ______________________________________                                    

Portion 1 is charged into a reaction vessel, equipped as describedabove, and is heated to its reflux temperature. The reaction mixture isheld under nitrogen during the entire reaction. Portions 2 and 3 areseparately premixed and added slowly simultaneously over a 60-minuteperiod while maintaining the reaction mixture at its reflux temperature.The reaction is continued for an additional 60 minutes. The Portion 4 isadded, and the reaction mixture is held at its reflux temperature for anadditional 30 minutes. Stripping of the reaction solvent is conductedsimultaneously with the addition of Portion 5 which is to replace thereaction solvent. When 533.00 parts of solvent are stripped and all ofPortion 5 is added to the reaction vessel, Portion 6 is added and thetemperature is brought to 115°-117° C. and maintained for 4 hours withcontinuous agitation. At the end of that period the epoxy number isdetermined. When the epoxy equivalent is zero or less than 1 epoxy unitper 500,000 gm, the reaction is finished. The solids content is 60%, andthe Gardner-Holdt viscosity at 25% reduction of solids with ethyleneglycol monoethylether is U to X.

PART III

A black pigment dispersion is prepared as follows:

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Solution by polymer prepared                                                                        371.00                                                  in Part II                                                                    Ethylene glycol monoethyl-                                                                          31.00                                                   ether                                                                         Carbon black pigment  31.80                                                   ______________________________________                                    

The above ingredients are premixed and charged into a conventional sandmill and ground at a rate of 30 gallons per minute while controlling thetemperature of the mixture below 70° C. The resulting carbon blackdispersion has about 58% solids content.

An extender pigment dispersion using lead silicate as the extenderpigment is prepared as follows:

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Solution polymer prepared                                                                           225.00                                                  in Part II                                                                    Ethylene glycol monoethyl-                                                                          110.00                                                  ether                                                                         Lead silicate pigment 206.00                                                  ______________________________________                                    

The above ingredients are premixed and charged into a conventional sandmill and ground at a rate of 30 gallons per minute while controlling thetemperature of the mixture below 70° C. The resulting lead silicatedispersion has about 63% solids.

PART IV

The electrocoating composition of a flated black paint is prepared asfollows:

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Portion 1                                                                      Resin solution of Part II                                                                          373.00                                                   Black pigment dispersion                                                                           97.00                                                    of Part III                                                                   Lead silicate pigment                                                                              440.00                                                   dispersion of Part III                                                        Benzoguanamine formaldehyde                                                                        76.00                                                    solution (XM 1125 produced                                                    by American Cyanamid Co.,                                                     85% in ethylene glycol                                                        monobutyl ether)                                                              Urea formaldehyde resin                                                                            100.00                                                   (Beetle-80, produced by                                                       American Cyanamid Co.)                                                       Portion 2                                                                      Deionized water      632.00                                                   Lactic acid 85% solution                                                      in water                                                                     ______________________________________                                    

Portion 1 is added into a mixing vessel, heated to 150° F. and mixed for3 hours, maintaining a temperature of 150° F. Portion 2 is added intoanother mixing vessel mixed for 10 minutes, and Portion 1 is added intoPortion 2 with continuous agitation. The pigmented water dispersion ismixed for 2 hours and diluted to about 15% solids with deionized water.

Industrial Applicability

The electrocoating composition, having a pH of 6.5-7.0 and aconductivity of 700-1000 micromhos, is charged into a stainless steeltank for electrodeposition. An untreated cold rolled steel panel or aphosphatized steel panel is positioned in the center of the tank,electrically connected to the negative side of a DC power source, andforms the cathode of the electrocoating cell. The tank is connected tothe positive side of a DC power source and forms the anode of the cell.A direct current of 150 volts is applied to the cell for 2 minutes at anambient temperature of 20°-25° C., and a paint film of about 0.6 mils isdeposited on the panel. The coated metal panel is removed from theelectrocoating cell, washed and baked at about 160° C. for 30 minutes.The resulting primer film has excellent adhesion to the metal substrate,is hard and has very good corrosion and saponification resistance overbare cold rolled steel and phosphatized steel. An acrylic enamel adheresto the primer film, and conventional acrylic lacquers can be appliedwith a conventional sealer coat over the primer to form a high-qualityfinish. Typical deposited films contain 90-95% solids.

This coating composition is particularly useful for priming automobileand truck bodies by electrodeposition for maximum corrosion protectionover all parts of the car including areas of poor phosphate pretreatmentor no pretreatment at all, due to its good throwing power of 13-15inches obtained with a standard automotive test method.

I claim:
 1. In a process for electrocoating with paint acathodically-charged substrate immersed in a coating bath containing anaqueous dispersion of said paint, said bath having a cathode zonecontaining said substrate and an anode zone containing a charged anode,the charged electrodes being maintained in electrical contact with eachother by means of said bath, wherein said bath comprises a cationicfilm-forming polymer, an acidic ionizing agent, the improvement whichcomprises:employing an organic acid which is volatile at temperaturesused to crosslink the film-forming polymer as the acidic ionizing agent;employing as the cationic film-forming polymer a graft copolymercomprising a mono-epoxide portion grafted onto an acrylic-amine backboneportion, which portions consist essentially of, by weight based on thegraft copolymer about:(a) 25-60% of an acrylic-amine backbone copolymercontributing:
 14. 7-35% of secondary amine acrylate or methacrylate,giving 0.08 to 0.2 equivalent of tertiary amine per 100 grams of graftcopolymer,7-17% of hydroxy-functional acrylate or methacrylate, 3-7.3%ethyl acrylate or methyl methacrylate, and 0.3-0.7% mercaptoethanol,giving primary terminal hydroxyl functionality, graft copolymerized with(b) and (c):(b) 33-60% of an epoxy-fatty acid copolymer of acondensation polymer of equimolar proportions of epichlorohydrin andbisphenol A, said condensation polymer being reacted with fatty acid inthe range of 1/1.4-1.7, and (c) 7-15% of a glycidyl ester of a tertiarycarboxylic acid containing 7 to 9 carbon atoms, and subsequently curingthe paint to crosslink the film-forming polymers.
 2. In a process forelectrocoating with paint a cathodically-charged substrate immersed in acoating bath containing an aqueous dispersion of said paint, said bathhaving a cathode zone containing said substrate and an anode zonecontaining a charged anode, the charged electrodes being maintained inelectrical contact with each other by means of said bath, wherein saidbath comprises a cationic film-forming polymer, an acidic ionizingagent, and a crosslinking agent, the improvement whichcomprises:employing an organic acid which is volatile at temperaturesused to crosslink the film-forming polymer as the acidic ionizing agent;employing as the cationic film-forming polymer a graft copolymer ofclaim 1, and employing as the crosslinking agent a composition which isnonreactive in the bath but reactive with said film-forming polymer atelevated temperatures to crosslink the polymers to form a durable paintfilm,and subsequently curing the paint to crosslink the film-formingpolymers.
 3. In a process for electrocoating with paint acathodically-charged substrate immersed in a coating bath containing anaqueous dispersion of said paint, said bath having a cathode zonecontaining said substrate and an anode zone containing a charged anode,the charged electrodes being maintained in electrical contact with eachother by means of said bath, wherein said bath comprises a cationicfilm-forming polymer, an acidic ionizing agent, and a crosslinkingagent, the improvement which comprises:employing an organic acid whichis volatile at temperatures used to crosslink the film-forming polymeras the acidic ionizing agent; employing as the cationic film-formingpolymer a graft copolymer of claim 1, and employing as the crosslinkingagent a composition which is nonreactive in the bath but reactive withsaid film-forming polymer at elevated temperatures to crosslink thepolymers to form a durable paint film,and subsequently curing the paintto crosslink the film-forming polymers by heating the coated substrateto a temperature of at least about 175° C. for at least about 30minutes.